Influence of Steam Treatment on Dye−Titania Complex Formation and Photoelectric Conversion Property of Dye-Doped Titania Gel

Xanthene dye molecules form a chelate complex with the titanium species on the titania surface in dye−titania systems. The complex formation causes a fast electron injection into the titania conduction band. In this study, simple spectroscopic and photocurrent measurements of the xanthene dye-doped titania gels prepared by the sol−gel method were conducted in order to clarify the influence of a steam treatment on the dye−titania interaction and electron transfer. The photocurrent quantum efficiency of the fluorescein-doped electrode was remarkably increased by the steam treatment compared to that of the untreated electrode consisting of an amorphous titania gel. The photocurrent action spectrum was red-shifted, and the short circuit photocurrent and open circuit voltage values increased with the steam treatment time. The steam treatment promoted the dye−titania complex formation, a negative shift in the conduction band potential of the titania, and the electron injection from the dye to the titania.